STAR-RIS-aided NOMA for Secured xURLLC

Short packet-based advanced Internet of things (A-IoT) calls for not only the next generation of ultra-reliable low-latency communications (xURLLC) but also highly secured communications. In this paper, we aim to address this objective by developing a non-orthogonal multiple access (NOMA) system with untrusted user. There exist two key problems: The confidential/private message for the far user will be exposed to the untrusted near user with successful SIC; The restrictive trade-off among reliability, security and latency poses a great challenge in achieving secured xURLLC. In order to solve these issues, we introduce simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS), which provides additional degree of freedom to enable a secure and fair decoding order and achieve a desired trade-off among reliability, security and latency. To fully reveal the trade-off among reliability, security and latency, we characterize the reliability and security via decoding error probabilities. A leakage probability minimization problem is modeled to optimize the passive beamforming, power allocation and blocklength subject to secure successive interference cancellation (SIC) order, reliability and latency constraints. To solve this complex problem, we explore its intrinsic properties and propose an algorithm based on majorization minimization (MM) and alternative optimization (AO). Simulation results demonstrate the validness of our study in this paper.

Parameter Design for Secure Affine Frequency Division Multiplexing Waveform

The secure affine frequency division multiplexing (AFDM) waveform design is a main concern in high-mobility networks. In this article, we employ the four key parameters in AFDM to design secure waveforms, and afterward we analyze the role of the four parameters to reveal the design guideline. We find that c1 is bounded by the Doppler shifts and preset guard. The parameter c2 exhibits a minimum periodicity of 1, with the effective range [0, 1] rather than any real number. The adjustable parameters c1 and c2 introduce additional degrees of freedom to the AFDM waveform, thereby enhancing the anti-eavesdropping performance. In addition, excessive Lmax that determines the preset guard interval leads to a security-risk interval and poses eavesdropping risks. Therefore, the optimal Lmax equals maximum delay. Numerical simulations verify the accuracy of our analysis.